Plant health monitor

Press, 31 August 1984, Page 19

Plant health monitor

Crops in Canterbury are generally well advanced and healthy, although in some areas the continual decline in the soil moisture levels is still causing concern, according to the M.A.F.

Irrigation has started on some lighter land. Farmers are advised to regularly check soil moisture deficits. Plan to start irrigating early before plant stress is likely to occur. Check all pesticide spray equipment now and give it a trial run. Inspect stocks of chemicals and forward order if necessary. Be sure to walk through all crops regularly from now on. Remember that control of pests and pathogens becomes more difficult and costly if damage occurs and continues unnoticed. CEREALS

Before attempting to control weeds, make sure thay are correctly identified. Only then can the best and most economic choice of herbicide and/or control programme be made. Your local M.A.F. office provides a weed identification service and advice on control measures.

© Perennial weeds: Begin control measures now to reduce problem perennial weeds such as yarrow and couch. Yield losses in spring can be avoided by applying Roundup followed by soil cultivation two weeks after spraying. 0 Take-all and grassgrub: The symptoms of grassgrub damage are similar to those

of take-all. It is important to accurately identify the cause of damage as a significant take-all problem can persist for some years. Check for blackened roots indicating take-all and note the incidence. Grassgrub problems are less significant. In both cases the application of extra nitrogen now to affected areas will help surviving plants compensate for damage. © Speckled leaf blotch: This disease is occurring on susceptible cultivars such as Kopara and Oroua. Control with a fungicide should be carried out before the end of tillering to make sure that the disease does not interfere with spikelet initiation, or carry through to produce further damage later in the season.

® Barley scald: Symptoms are beginning to show up in early sown crops. In susceptible cultivars, buildup should be monitored closely. If the weather is cool and damp and the disease is observed on top leaves, apply fungicide to control the disease.

® Stripe rust in wheat: Seedling symptoms are ap-

pearing on autumn sown crops that did not have a protective seed dressing. These should be foliar sprayed to stop a build-up of innoculum.

Other crops whould be monitored carefully from now on to detect first signs of the disease.

The Lincoln College Agricultural Microbiology Department has developed a monitoring -threshold-deci-sion making plan for stripe rust. The method makes monitoring less tedious and more accurate. Details from your local M.A.F. office.

® Seed treatment: Farmers who keep their own seed should decide soon whether to treat the seed. If a line has a clean history there should be no need to treat every year. If treated, ensure the chemical applied is effective on all smuts and net blotch in barley. Farmers using home grown seed must be more diligent monitoring crops and note all disease so that appropriate seed treatment chemicals can be used. Lucerne

Sitona larvae are starting to appear in the soil now. These will have developed from eggs laid in the autumn. Larval densities are not yet high enough to cause a problem. Numbers will, however, increase from now on and peak about December, especially in unsprayed, immature stands on light soils. There are no specific control measures for sitona larvae.